1. Field of the Invention
The present invention relates to chain saw having a two-cycle or two-stroke engine. The present invention also relates to a hand-held power tool such as a chain saw, trimmer, or power cutter having a two-cycle or two-stroke engine. The present invention further relates to a method for the construction of a hand-held power tool such as a chain saw, trimmer, or power cutter having a two-cycle or two-stroke engine.
The subject of the invention also refers to a crankcase scavenged internal combustion engine, mainly intended for a handheld working tool, such as a chain saw, with an engine body comprising at least one crankcase body and a cylinder body, which are joined together, and the engine is equipped with so called elongated scavenging dues, which over some part of their length, i.e. a crankcase part, extend in the crankcase body and have their inlet there, and over another part of their length, i.e. a cylinder part, extend in the cylinder body. Generally the crankcase scavenged internal combustion engine is of two-stroke type, but it could also be a four-stroke engine as well as other applications not only meant for a handheld working tool.
2. Background of the Invention
Chain saws and other handheld tools, such as hedge or weed trimmers and power cutters, such as those used for cutting dry wall, are usually designed with consideration to convenience of use as well as other factors. One important factor is the overall weight of the chain saw or handheld tool since, obviously, a person using the tool must hold it for periods of time. An excessively large or heavy tool would be unwieldy and tiresome for the user to hold for an extended period of time. In that regard, many handheld tools utilize an internal combustion engine that is lightweight and easy to manufacture, usually a two-stroke or two-cycle engine.
Unfortunately, two-stroke or two-cycle engines sometimes can produce substantial amounts of pollutants or other emissions. They also can sometimes be inefficient with respect to fuel consumption. It therefore becomes advantageous to develop a two-stroke engine that has reduced emissions and improved fuel efficiency, yet at the same time is still lightweight and easy to manufacture.
Crankcase scavenged internal combustion engines with so called elongated scavenging ducts, i.e. scavenging ducts starting in the crankcase part, usually in its lower parts, are known since a long time. The elongated scavenging ducts will under certain conditions have a favorable effect on the scavenging and can thereby reduce both the fuel consumption and the exhaust emissions. The scavenging ducts in the crankcase part are produced in that a vertically-split crankcase is provided with cavities on both sides of the parting plane. When assembling the crankcase a large continuous scavenging duct is thus created by both of the cavities. In case the sealing in the parting plane is drawn right up to the inner side of the crankcase it will split the large duct into two scavenging ducts which often is preferable. Generally the inlet of the scavenging duct is formed already during the casting process.
This is rational from a production point of view but it requires a specific crankcase for each motor application with varying placement of the inlet. It is therefore preferable to adapt the length of the scavenging duct and/or the cross-section area of each application in order to, in this way, obtain optimum engine performance. Such an adaption for a specific crankcase can be achieved essentially only by machining the inlet of the scavenging duct instead of pre-casting it and this is costly. In the vertically-split crankcase a bearing position for each crankshaft bearing is positioned in each of the crankcase halves.
There are also internal combustion engines having a so called horizontally-split crankcase. It means that the crankcase is split at the center axis of the crankshaft and comprises essentially only one part. In that case a cylinder part contains the top crankcase half down to the center axis of the crankshaft. In this manner the engine body is thus made of only two parts instead of three when a vertically-split crankcase is used. The bearing positions of the crankshaft bearings are thus positioned in each part of the engine body and the bearings are clamped between the engine body parts. The applicant does not readily know of any example of an internal combustion engine with a horizontally-split crankcase having elongated scavenging ducts, even if this is preferable from many aspects.
The purpose of the present invention is to substantially reduce the above outlined problems, and to achieve advantages in many respects.
The above mentioned purpose is achieved in a crankcase scavenged internal combustion engine in accordance with the invention and having the characteristic features as described in the features of the invention herein below.
The crankcase scavenged internal combustion engine according to the invention is thus essentially characterized in that the crankcase part of at least one scavenging duct to a great extent comprises an insert part with at least one inner wall facing the crankshaft assembly and provided with the inlet, so that the crankcase part of the scavenging duct is comprised of the insert part alone or in combination with the inner side of the crankcase body, and leads from the inlet to an outlet intended to connect to the cylinder part of the scavenging duct. Through this insert part with the inner wall facing the crankshaft assembly and provided with the inlet of the scavenging duct, possibilities are created to supply a horizontally-split crankcase with scavenging ducts in the crankcase part so that elongated scavenging ducts are achieved. For a vertically-split crankcase, this insert part implies improved flexibility. Since the inlet of the scavenging duct is located in the inner wall of the insert part, the inlet of the scavenging duct can be moved by replacing the insert part. This means that with the aid of several different insert parts a specific crankcase can be adapted for many different motor applications. Adaption of both length and/or area of the scavenging ducts can be made, so that many different ratios of length/area of the scavenging ducts are achieved. Obviously this is a big advantage, both for a horizontally-split and for a vertically-split crankcase, since it offers opportunities, both in the development stage and in the serial production, to make changes quickly and easily.
To further explain, the scavenging ducts can be configured in many different dimensions and/or shapes to achieve or modify different engine characteristics. The length, width, depth, cross-sectional area and/or shape of the duct can be modified to effect engine tuning, horsepower, range of revolutions per minute (RPM), torque, and, as discussed above, fuel consumption and emissions. The scavenging duct can therefore be designed in particular shapes and sizes depending on the engine and its desired engine characteristics.
Further, the insert allows for tailoring of the engine with the same crankcase. The insert can be modified, while the crankcase can remain the same. Thus, production costs can be reduced because different crankcases will not have to be produced for each individual engine if the engine requires different engine characteristics, such as piston structure, cylinder displacement, and shifting the RPM at which a desired horsepower or horsepower curve(s) are generated or at which a desired torque or torque characteristic are desired. Therefore, even with the same cylinder and piston, the characteristics of a two-stroke engine can be changed by changing the various parameters as indicated in the above paragraphs.
Further, in at least one possible embodiment, the scavenging duct can extend around a substantial portion of the crankcase body to further achieve different engine characteristics as described above. For example, the scavenging duct could extend past the six o""clock position at the bottom of the crankcase up to, for example, the eight or eight-thirty position near the side of the crankcase.
Also, the insert can provide advantages relating to cost over cast crankcases. Cast crankcases can be extremely expensive to produce with some degree of precision. An insert can be modified as discussed above, but can be used on the same crankcase. Thus, only one crankcase type may need to be made, thereby reducing cost by avoiding the casting of different crankcases for particular uses.
Such an insert of the type described above is manufactured by Veinge Plast, which is a manufacturer located at Kraftgatan 1, 31234 Laholm, Sweden. Although the insert can be made from a variety of materials, such as plastic or metal, a type of plastic that can preferably be used in making the insert, according to at least one embodiment of the present invention, is a plastic material called xe2x80x9cAkulon.xe2x80x9d Akulon is produced by a company called DSM, whose home office is located at Het Overloon 1, 6411 TE Heerlen, the Netherlands. Akulon comprises two main components, namely Polyamide 6, which is also manufactured by DSM, and 45% added glass fiber (PA6+45% GF). DSM also has an internet world wide web (WWW) site that provides summaries and information regarding its products, such as Akulon and Polyamide 6, and services. The address of DSM""s web site is xe2x80x9chttp://www.dsm.nlnxe2x80x9d.
The insert can be used, as discussed above, in engines in a variety of machinery, such as chain saws, hedge and weed trimmers, power cutters, leaf blowers, and possibly even lawn mowers. Husqvarna AB is a company that produces such machinery that could use the insert. Husqvarna AB""s mailing address is SE-561 82 Huskvarna, Sweden. Husqvarna AB""s internet web site address is xe2x80x9chttp://international.husqvarna.comxe2x80x9d. Many examples of different machinery and products that could use an insert as described above can be found on the web site and in Husqvarna product catalogs that can be obtained from the company.
The above-discussed embodiments of the present invention will be described further hereinbelow. When the word xe2x80x9cinventionxe2x80x9d is used in this specification, the word xe2x80x9cinventionxe2x80x9d includes xe2x80x9cinventionsxe2x80x9d, that is the plural of xe2x80x9cinventionxe2x80x9d. By stating xe2x80x9cinventionxe2x80x9d, the Applicant does not in any way admit that the present application does not include more than one patentably and non-obviously distinct invention, and maintains that this application may include more than one patentably and non-obviously distinct invention. The Applicant hereby asserts that the disclosure of this application may include more than one invention, and, in the event that there is more than one invention, that these inventions may be patentable and nonobvious one with respect to the other.